1. Field of the Invention
The present invention relates generally to testing of a digital image of a digital device and, more particularly, to a device and method for equalizing illumination of light sources for a digital image test member and an apparatus and method for testing the color of a digital image using the same.
2. Description of the Related Art
In every object, the intrinsic color thereof and the color of light radiated onto the object are mixed together. Human vision can detect only the color of an object. For example, human vision perceives the green color of leaves on trees to be almost the same in the morning, in the afternoon, and at dusk. In contrast, a complementary metal-oxide semiconductor (“CMOS”) image sensor detects and represents a color in which the color of an object itself and the color of light are mixed together. The difference between the color of an object as detected by a human's unaided eyes and the color of the object as detected by a CMOS image sensor results from the difference in the detection of color.
Due to the difference in the detection of color between a CMOS image sensor and a human's unaided eyes, it is necessary to understand and freely adjust the characteristics of a physical value for the color of light, that is, a color temperature represented in Kelvins, at the time of artificially establishing environmental settings for testing a CMOS image sensor.
If it is impossible to freely adjust color temperature varying with light source at the time of image testing for a CMOS image sensor in a range of implementation of a minute light source (low luminance: <1˜30 Lux; normal luminance: 30 Lux˜) in steps, light gradually changes from dark brown color to orange, yellow, white, and blue color series as color temperature decreases or increases. Since an image viewed through a CMOS image sensor is changed in the above manner, it is difficult to accurately and precisely determine the characteristics of the image itself as received by the CMOS image sensor.
In the case where, in order to artificially construct the environment of solar light at noon, 3200K is obtained using tungsten lamps, and various illumination (unit: Lux) environments are set up by adjusting the light sources in specific steps, an increase in color temperature causes the overall image to tend toward a blue color series and a decrease in color temperature causes the overall image to tend toward a red color series, even though the illumination is the same.
Due to the above image variation, it may be difficult to perform accurate image tests. When artificial light sources are constructed, such image variation attributable to color temperature variation is a significant problem.
In the case of image testing, the reproduction of white, rather than a specific color, is emphasized, and what is signified by white must be precisely defined. In the case of a CMOS image sensor, white balance is adjusted generally in the early state of color tuning. At this time, the functions of the CMOS image sensor, such as gain or black level, are adjusted such that red, green, blue (“RGB”) signal ratios are equalized on the basis of line-up charts, such as a Grey Scale Chart, a White Chart, and a Color Checker, onto which appropriate light is radiated. In other words, the entire image of the CMOS image sensor is produced with reference to an achromatic color such as white or grey. An achromatic color intrinsic to the Grey Scale Chart or White Chart is apparently not changed, but the overall color of an image appears different due to the color of specific light that is radiated onto the achromatic color.
In the image tests of a CMOS image sensor under various light sources (low luminance region: 1˜30 Lux; normal luminance region: 30 Lux˜), the entire image is determined by light that is radiated onto a line-up chart.
Accordingly, it is difficult to conduct the accurate characteristic tests of an image itself appearing via the CMOS image sensor and to construct an environment for starting color tuning due to color temperature variation. As described above, the most convenient way to define the color of a light source is to use color temperature.
Currently, when light sources are artificially implemented, tungsten lamps having color temperature characteristics most similar to those of solar light are widely used. For example, when an artificial environment is set up using a tungsten lamp having 3200K color temperature characteristics and tests are conducted at fixed illumination without varying illumination in steps, the difference in the color of an image, attributable to variation in color temperature, does not appear.
However, in the image tests of the CMOS image sensor, illumination must be adjusted in steps for specific color temperature regions capable of producing various environments, for example, morning, a clear and blue sky, a cloudy and blue sky, noon, and sunrise and sunset, so that color temperature variation depending on light source, that is, color temperature variation attributable to stepwise illumination adjustment, causes overall image distortion.
Since a camera mounted in a mobile phone, which is a representative application system to which CMOS image sensors are applied, is not used under the same conditions and in the same environment by users, it is necessary to set up various artificial environments and to test the camera using various methods.
Currently, tungsten lamps, which are most widely used as artificial light sources, have an advantage in that they can most closely realize the color temperature of solar light (a color rendering index of 95%). However, in the construction for the testing of CMOS image sensors, color temperature abruptly varies at the time of implementing various environments and adjusting illumination over a precise and wide range, therefore the types of lamps that are capable of implementing various color temperatures are limited.
Although correction may be forcibly made using various filters, e.g. color temperature blue (“CTB”), color temperature orange (“CTO”), neutral density (“ND”), such that color temperature is made uniform, the range of implementation of color temperature of a tungsten lamp and a high amount of heat of a tungsten lamp are limitations to the construction of an artificial light source.